1. Field of the Invention
The present invention relates to a storage device and a device changeover control method for storage devices.
2. Description of the Related Art
As a storage device, there may be provided a storage region using a RAID (Redundant Array of Independent Inexpensive Disks) in which disk drives such as for example hard disk drives or semiconductor memory devices are arranged in array fashion. A host computer (hereinbelow called “host”) performs data reading and writing by accessing a logical storage region provided by the storage device.
A storage device is required to have high usability and high reliability. To achieve this, it is known to protect against occurrence of faults by constituting a disk array using a plurality of mirror disks that mirror the current disk and standby disk (Laid-open Japanese Patent Application No. H. 7-129331). In the technique disclosed in this reference, when it is anticipated that a fault may occur, the disk that is the source of data reading is arranged to be changed over from the current disk to the standby disk. It should be noted that the technology disclosed in this reference merely discloses respective mirroring simply of the various constituent elements of the disk array; it does not disclose changeover of a volume logically provided on a physical storage region.
The host may change over the volume (LDEV: logical device that is used for various reasons. When an LDEV is changed over, the currently used LDEV and the LU (logical unit) must be disconnected and a new LDEV connected with this LU. However, since the LU that is disconnected from the LDEV temporarily loses recognition from the host, during the period until the changeover of LDEV is completed, recognition of the LU by the host is temporarily interrupted.
If fault monitoring software or the like is operating on the host, there is a possibility that the interruption of recognition of the LU during LDEV changeover may be detected by the fault monitoring software as occurrence of a path fault. Also, if the host OS is Windows (registered trademark), the interruption of recognition of the LU during LDEV changeover may cause so-called PnP (plug-and-play) to occur.
Accordingly, if an LDEV changeover operation is performed during execution of a data processing task by the host, there is a possibility that the disconnection of the LU and the LDEV by this changeover operation will be recognized by the host and may affect the task of data processing on the host.